About 1995 I used 24 gauge hardware cloth ("screen") which I cut to shape. Then I spread Riccia below it. The Riccia eventually grows through the screen to form a lawn like appearance. It needed to be "mowed" with scissors to give it the flat appearance and to make it fill in the entire screen area. Riccia floats as a mechanism designed to allow it to survive when various physical catastrophes occur in its environment. The cuttings float to the top and grow giving new material to fill in the screen. It takes some work but it seemed worth it. When the "lawn" is complete you will not be able to see the screen except at the very edge in spots. Since Riccia likes bright light, the plant below the screen will eventually die.
That is a good time to replace the screen, and the Riccia will start to disconnect and float away. This is the reason I kept trying to find a better way to use it. Today you can find plastic screens on line for this purpose.
An alternative to this screen is the screen like material found in craft stores which has the additional benefit of coming in green so as to be less obtrusive. The problem with this is that the Riccia is a strong floating plant and the screen is only slightly heavier than water making it necessary to hold it down, which then distracts the eye in a different way. ELB, however, have the habit of picking at every thing and soon started to pick apart the bottom Riccia. Additionally, they periodically became trapped under the screen and several died. So I gave up this method and began to place the Riccia under the root of Anubias since I often have Anubias growing on wood or rocks.

(Some Riccia can be seen here in the Anubias and even floating up into the crypts.
Recently (March 2007) I created a moss wall with Anubias. I went to my home improvement store and purchases a black plastic landscape screen. I cut two pieces the size of my back wall less one inch off the sand bottom. I purchased several suction cups from the craft store which has metal hooks on them. I removed those hooks and inserted the bulbous tip which held the hooks through the screen by snipping on segment of the screen. This would then hold the screen to the aquarium back.
I laid the two screens on top of each other and passed black twist ties through to bind it. So the screen would not lie flat I passed the twist ties through the first layer crisscrossed the ties, then put them through the second layer before tying them together. These must be put together in one specific direction and this caused that direction to be reversed, so, the first time I put these through backwards, so, once crossed, they would lock together.
This created a space between the layers into which I placed various mosses, Java Moss, Christmas Moss, Pella, and a Fissidens, and so on. After I placed this into the tank I hooked Anubias roots into the screen, and used a few of the hooks off the suction cups to hold several onto the screen.

It looks great! Everything is growing well on the wall.
This adds tremendous plant mass to the tank enabling even better filtration for the tank by eliminating nitrogen.

Some background:
Riccia fluitans is a thallose liverwort that repeatedly forks into two sections and belongs to a group of plants called Bryophytes which also includes mosses, hornworts. Bryophytes are broken up by Mishler et al. Into three groups: Bryophyta, the mosses, Jungermanniophyta the liverworts, and Anthocerotophyta the hornworts. Within Jungermanniophyta is the family Ricciaceae which Howe treats as the three genera and 27 species. There are Riccia that live in many diverse environments from fully aquatic to desert sand dunes, most of which are terrestrial. The genus includes species such as Riccia rhenana (also used in some aquariums), Riccia beyrichiana, Riccia bifurca, Riccia cavernosa, Riccia ciliata, Riccia crystallina, Riccia elliottii, Riccia frostii, Riccia glauca, Riccia huebenerana, Riccia rhenana, Riccia sorocarpa, Riccia sullivantii, and Riccia violacea. Some of these are overlapping names according tot he specifics of the taxonomy established by various groups.
Riccia fluitans is found all over the world (except by the poles), it is truly cosmopolitan. From fens in England to bogs in New England to prairie marshes in North Dakota, to mud flats in Australia and the subantarctic environment of Macquarie Island and palustrine wetlands in New Zealand, it is found on every continent except antartica. (It's almost like there was a big flood that carried it all over the world and made huge fossil beds.) It is found in very diverse areas as a margin plant, that is, by water's edge and on either the terrestrial or aquatic side and down into the deeper areas of ponds and streams, both temporary and permanent water sites, both acidic and brackish. Riccia seems to need water and light to grow, and that is about all.
They are considered “simple” plants since they do not have, flowers, seeds, and most have no vascular system, though the two varieties used in aquariums are vascular. (If you think it is simple, you try making one!)  Those that have a root like system (called rhizoids) serve both as a method of attachment and for nutrient absorption. Riccia fluitans can develop rhizoids in the right environment.
A rhizoid is a single elongated cell that is specialized for absorption in those liverworts that have vascular systems such as Riccia fluitans. Those that lack this capability are usually only one cell thick so each cell directly absorbs nutrient from its environment. The vascularized liverworts also absorb directly, this is why they respond so quickly to sodium bicarbonate and nitrogen added to the tank.
Riccia usually lives in the mud and silt of rivers, streams, and bogs. Bogs are ombrotrophic, that is, deriving their water from rainfall.
Riccia prefers CO2 as a carbon source for photosynthesis as opposed to bicarbonate, however, a higher amount of bicarbonate results in higher levels of carbon dioxide. In fact there is evidence that it will not use bicarbonate at all, lacking the needed enzyme to absorb it. Carbon dioxide needs no enzyme to be absorbed, but is taken in as a gas in solution. Therefore, if you are adding bicarbonate to your tank with Riccia, the biological filter is your best friend as the bicarbonate increases the carbon dioxide cycle which feeds the Riccia.
Riccia fluitans, while not a bunch plant (that is, those plant sold in bunches at the aquarium shop), does, with adequate lighting, produce more oxygen than any other plant. This is best done by simply pushing it into the bottom gravel using a small tool. I use a piece of bamboo that has been sharpened to a very blunt forked point. I used bamboo because I was looking for just the right tool and realized the only thing I had on hand at the time was the bamboo goring in a pot in my yard. Why pay for an expensive tool when this works quite well? Inserting the Riccia using this tip then removing it suddenly with a jerking action allows the gravel to hold the Riccia down (the gravel moves faster than the Riccia). After this you keep repeating this step as needed and trim off excessive growth.
There are other ways of growing Riccia. Many a web page recommends tying the Riccia to a piece of wood of rock using fishing string to secure it. This is an older method that has been used for years, since about 1935 in fact.  The benefit to this is that you can rearrange your aquarium by moving the rock or driftwood logs. Some people tie all plants to rocks or wood so rearrangement is easy. Trimming these is as easy as buying a long pair of scissors such as barber's scissors. Trimming is also necessary to keep the plants under the string alive as they will otherwise die from lack of light.
So I tried the rock method using different netting materials. The best would be fishnet nylons, but I never found them before it struck me that the anaerobic environment at the bottom of the tank would work all by itself. I started immediately and in a short time I had the desired look. 

Ah ha! Great results! Fast growing Riccia to fill in my blank spots and all the other plants started to bubble also indicating rapid photosynthesis, therefore, rapid growth. Even my Java Fern had bubbles on it. During this odyssey I also built my own light fixture so now I have 200 watts of fluorescent light in a 60 gallon tank. This didn't hurt! But the bubbles didn't start until my mixture of fertilizer hit the water. Now, every night I have bubbles on my plants. This is good. What is the mixture I used in my fertilizer you ask? Basically Sodium and Potassium bicarbonates. When I added urea for nitrogen (basically nitrogen bicarbonate) and epsom salts (magnesium sulfate) to the tank the growth was huge. So was the algae growth. I have recently (2007) taken to adding potassium bicarbonate, magnesium sulfate, bone meal and blood meal at a rate of about 2 grams per day to the tank. The plants are growing well and there is little algae growth.

Blood meal adds notrogen and bone meal, calcium phosphate. This seems to be working well, but it requires I change the water more frequently than before to prevent toxic levels of metals from accumulating in the tank.

Time will tell.